Historically, dye-type thermosensitive paper containing a colorless leuco dye and a phenolic acidic substance was developed as a thermosensitive recording technology by NCR Inc. in 1960s, and this system has become the mainstream of a thermosensitive recording systems. Thereafter demands for thermosensitive paper (hereinafter referred to as “thermosensitive recording material”) have increased rapidly (1) since miniaturization and price reduction of apparatuses became possible due to development of thermal heads based on semiconductor technologies and significant improvement in cost and performance; (2) since, high quality (high sensitivity, improvement of head matching property, etc.) of thermosensitive paper (thermosensitive recording material) itself was realized; and (3) since the thermosensitive recording system was evaluated to be advantageous in view of user-friendliness, i.e., convenience, low costs, freedom from maintenance, etc. as compared to other recording systems such as static recording, ink jet recording, PPC recording, etc.
However, as thermosensitive recording materials are used for facsimiles, various printers, etc. and have become familiar to daily life, defects of thermosensitive recording materials have been also recognized well. Namely, the following defects have been pointed out:    discoloration by light;    discoloration during storing at high temperature (being left in a vehicle, etc.);    fading of a recorded image by chemical agents such as a plasticizers in wrapping films, oils, organic solvents in marker pens, ink for ink jet printers, etc.;    a lack of plain paper-like feeling (good stamping property such as good drying of stamps, etc., a matted recording surface which is easy to read, good writing property with respect to a pencil, etc., resistance to staining by friction, etc., and so forth), etc.
Therefore, development and provision of a thermosensitive recording material free from the above-mentioned defects and having high value have been required.
Recently, thermosensitive recording materials have been widely used since they are relatively inexpensive and recording apparatus therefor are compact and freedom from maintenance. Under such circumstances, competition in the market of thermosensitive recording materials has become fierce, and demand for thermosensitive recording materials having higher performances that are different from those of conventional ones, and specifically thermosensitive recording materials having high density of developed color, whiteness of background, sharpness, storage stability, good hue and sharpness for a full-color image printed by an ink jet recording system, etc. has increased. Therefore, intensive investigations concerning various performances such as color developing property, storage property, etc. of thermosensitive recording materials are now being conducted in order to satisfy such demands.
The performances that the thermosensitive recording materials should have include, for example, (1) high sensitivity (capability to provide high density); (2) high whiteness of a background portion (non-printed portion) (low background fogging); (3) superior image storage property after photographic printing; (4) superior light fastness; (5) superior resistance to chemical substances; (6) sharpness and high image quality; (7) good hue and sharpness of colors for a full-color image printed by an ink jet recording system; (8) good thermal head matching property and head resistance property by which thermal head abrasion is decreased; (9) plane paper-like feeling; (10) printing applicability that enables printing on a thermosensitive recording layer, and stamping property free from bleeding; (11) applicability for high performance printers such as a high speed printer, etc.; and (12) environmental applicability, etc. Under the above-mentioned circumstances, it is required that all of these performances are simultaneously satisfied without deteriorating any of the performances. However, under the present circumstances, a thermosensitive recording material that can satisfy all of the above-mentioned performances simultaneously has not been provided yet. In particular, the following points can be conspicuously noted.
For instance, although high-speed printing (photo printing) is demanded in fields such as use for receipts in POS (point of sales) registers, a problem exists in that when high-speed printing is performed in general, head contamination is easily caused, and consequently, print quality is deteriorated as a result of the head contamination. In particular, in recent years, in order to reduce the production cost, a printer which can selectively use a thermal transfer recording is provided. However, the printer is provided with a thermal head having a so-called partial glaze structure to impart a thermal transfer recording capability. As a result, in particular, the printer has the tendency to cause head contamination when high-speed printing (photo printing) is performed on the thermosensitive recording material.
Although stability which can stably maintain recording for a long period of time, that is, image preservability with respect to temperature and humidity conditions, and stability of an image (plasticizer resistance and chemical resistance) with respect to a plasticizer or the like are very important in fields such as use for receipts in the POS registers, a thermosensitive recording material which can always sufficiently maintain a formed image has not been provided up to now.
On the other hand, Japanese Patent Application Laid-Open (JP-A) No. 6-135159 discloses a thermosensitive recording material containing a salicylic acid derivative and/or metal salt thereof having an aryloxyalkyloxy group as a substituent as an electron-accepting compound, whereby chemical resistance is improved. However, image density and head contamination (high-speed print capability) or the like at the time of high-speed printing are insufficient, and improvement is further required.
Furthermore, such system also has a problem in view of (13) ink jet applicability. Namely, full color information is sometimes recorded on a thermosensitive recording material using ink for ink jet printing. However, when ink jet printing is carried out on a recording surface of a conventional thermosensitive recording material containing bisphenol A, hues of ink cannot be reproduced faithfully, and sharp hues can not be obtained. Further, when an image is already formed on the recording surface by thermosensitive recording, the image sometimes fades. Furthermore, when the above-mentioned conventional thermosensitive recording material is placed in contact with a medium having an image printed thereon by an ink jet printer, background fogging or fading of the recorded image sometimes occurs.